1. Field of the Invention
The present invention relates to a variable optical attenuator, and more particularly to a variable optical attenuator of optical path conversion (hereinafter will be referred to as a path-converted variable optical attenuator) that adopts a Micro Electro Mechanical System (MEMS) type and reflects optical signal launched from the transmitting fiber to the receiving fiber to a separate path from paths of transmitting/receiving fibers so that attenuation may not change according to wavelength.
2. Description of the Related Art
In general, an optical attenuator as one of optical communication instruments artificially adjusts the intensity of incident light for a certain magnitude to cause optical loss so that a beam of attenuated light may emerge from the optical attenuator. Accordingly, the optical attenuator optimally adjusts the intensity of light incident on a light receiving element so as to be used in an optical communication network or an optical measuring instrument.
The optical signal attenuator for optical communication is an optical component having a set of input and output waveguides for causing a certain magnitude of optical loss to input light and outputting attenuated optical power.
In the optical communication, the optical communication power level is different according to a system configuration and includes the difference in transmission loss of optical fiber due to transmission distance, the number of optical fiber coupling portions, the number and performance of optical components such as optical divider/coupler used in transmission lines. When the optical receiving level is excessive, the optical attenuator is used for adjustment of the optical receiving level.
In addition, the optical attenuator has representative applications such as estimation, adjustment and correction about the communication instruments or the optical measurement instruments.
According to the aspect of functions thereof, the optical attenuator can be classified into a fixed optical attenuator for applying a certain quantity of attenuation to light, and a variable optical attenuator (VOA) capable of varying the quantity of attenuation.
Also, it is important for the optical attenuator to have the fixed quantity of attenuation according to wavelength in the used wavelength range.
The variable optical attenuator of the prior art is generally classified into a waveguide-type attenuator using a thermo-optic effect of silica or polymer-based material, a mechanical connector-type large-sized attenuator and an MEMS attenuator using an MEMS actuator.
FIGS. 1 and 2 schematically show a shutter-type MEMS variable optical attenuator of the related art.
The reference number 41 designates a transmitting fiber, 42 designates a receiving fiber, 43 designates a movable shutter, 44 designates connecting means, and 45 designates a shutter portion of the movable shutter 43.
FIG. 1 depicts the shutter-type MEMS variable optical attenuator of the prior art before the movable shutter is operated, in which transmission is made from the transmitting fiber 41 to the receiving fiber 42 without attenuation of an optical signal.
FIG. 2 depicts the shutter-type MEMS variable optical attenuator of the prior art after the movable shutter is operated, in which the optical signal is transmitted from the transmitting fiber 41 to the receiving fiber 42 after being attenuated as much as screened by the shutter portion 45.
In such a shutter-type MEMS variable optical attenuator, the movable shutter 43 is positioned between a pair of transmitting/receiving fibers and the connection area between the two optical fibers 41 and 42 is adjusted according to displacement of the movable shutter 43 in order to control insertion loss.
However, such a shutter-type variable optical attenuator has a drawback that the optical signal returns to the transmitting fiber 41 reflected from the movable shutter 43 in which the influence of the returning optical signal should be minimized.
FIGS. 3 and 4 schematically show a micro-rotational mirror-type MEMS attenuator of the related art, in which the reference number 51 is an input fiber, 52 is a lens, and 54 is an output fiber.
FIG. 3 depicts the micro-rotational mirror-type MEMS attenuator of the prior art before the mirror is inclined, in which an optical signal from the input fiber 51 is focused through the lens 52, reflected by the mirror 53, and then focused through the lens 52 again to proceed into the output fiber 54 without being attenuated.
FIG. 4 depicts the micro-rotational mirror-type MEMS attenuator of the prior art after the mirror is inclined, in which the optical signal from the input fiber 51 is focused through the lens 52, reflected by the inclined mirror 53, and then focused through the lens 52 to proceed into the output fiber 54 as attenuated as much as the mirror is inclined.
Accordingly, in the micro-rotational mirror-type variable optical attenuator, the input/output optical fibers 51 and 52 are connected using reflection of the mirror and each displacement of the mirror is used to control insertion loss.
However, such a micro-rotational mirror-type variable optical attenuator has a drawback that the mirror 53 should be mounted parallel to the substrate so that a difficult packaging is required in which the optical fibers is perpendicularly assembled to the substrate.
Also, even the variable optical attenuator of the same MEMS type can have a difference in performance according to the configuration and shape. Also, in the MEMS structure, the optical fiber, micro-mirror, lens and so on require precise alignment, and in the aspect of the device, it is advantageous to arrange the optical fiber parallel to the substrate rather than to arrange the optical fiber vertical to the device substrate.
However, in the rotational mirror-type MEMS variable optical attenuator, manufacture of the rotational mirror and use of a collimator lens are necessary and a structure of arranging the optical fiber vertically to the substrate is required. On the other hand, while the structure of the shutter-type MEMS variable optical attenuator does not require the collimator and the optical fiber can be arranged parallel to the substrate, light reflected from the shutter returns to the transmitting fiber causing a noise signal.
Accordingly, the present invention has been proposed to solve the foregoing problems of the prior art and it is an object of the invention to provide a path-converted variable optical attenuator which adopts an MEMS type and reflects an optical signal to a separate path from paths of transmitting/receiving fibers, when the optical signal of the transmitting fiber emerges to the receiving fiber, so that attenuation may not vary according to wavelength.
According to an embodiment of the invention to solve the foregoing object, it is provided a path-converted variable optical attenuator comprising: a transmitting fiber for launching an optical signal through a transmitting core; a receiving fiber for receiving the optical signal from the transmitting fiber through a receiving core; and a mirror having a reflector for obstructing the optical signal launched from the transmitting core of the transmitting fiber from proceeding into the receiving core of the receiving fiber, and being displaced in a direction allowing a portion of the optical signal of the transmitting fiber into the receiving fiber to attenuate the optical signal.